Similar case search apparatus and method, and recording medium storing program therefor

ABSTRACT

More accurate search for similar cases can be carried out in the case where images at different time phases exist. A contrast enhancement information analysis unit obtains time phase information of search target images obtained at different time phases in the same examination from accompanying information of the images, and a similar case database storing similar case information sets each including examination ID, time phase information, a characteristic quantity, and image interpretation/diagnosis support information is searched in processing by a first similar case information search unit, a second similar case information search unit, and a judgment unit. A corresponding portion of the similar case information sets satisfying three conditions comprising agreement of the time phase information with the search target images, agreement of examination between the portion of the similar case information sets, and similarity of a content-based characteristic to the search target images is obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method for searchingfor information of cases similar to a search target medical image, andto a recording medium, in which a program causing a computer to executethe method is recorded.

2. Description of the Related Art

In order to support interpretation of medical images by physicians anddiagnosis carried out by clinicians based on medical images, similarcase search systems have been proposed. In such systems, medical images,information including interpretation results and diagnosis resultspertinent to the images, and the like are stored in databases, and thedatabases are searched for images similar to medical images as targetsof image interpretation/diagnosis and for information such as results ofimage interpretation/diagnosis pertinent to the similar images.

For example, a system is known wherein an image database storing imagedata sets representing images of subjects is searched for similar imagedata sets having regions whose pictorial characteristic is similar to animage data set inputted as a search target and a result of the search isoutputted (see U.S. Patent Application Publication No. 20040003001, forexample).

In addition, a similar medical image search apparatus having a similarmedical image database is known (see Japanese Unexamined PatentPublication No. 2004-173748, for example). The similar medical imagedatabase relates to each other the types of operations for judgmentprocessing used at the time of detection of shadows of foci included inmedical images, a characteristic quantity of the shadows of foci foundin the judgment processing, and the medical images. The similar medicalimage search apparatus searches the similar medical image database basedon a result of the same judgment processing carried out on one of aplurality of interpretation target images.

In medical imaging, lesions are identified in many cases by obtainingtemporal change images of the same body part associated with infusion ofa contrast material, that is, images at different times. For example, inthe case of examination to identify a liver tumor by use of CT,difference in spread of a contrast material is observed between imagesof four temporal changes comprising a pre-contrast phase image (plainCT), an early phase image (an arterial phase image), a portal phaseimage (a portal venous phase image), and a late phase image (anequilibrium phase image), and judgment is made on distinction betweenveins and the tumor and on progress of the disease.

A region of liver tumor has small differences in CT values from othernormal liver regions. In addition, the region in an image obtained at asingle time phase is sometimes extracted as a region similar tosurrounding veins, depending on how a contrast material has spread.Therefore, a plurality of images at different time phases need to beobtained for comparison of complex changes associated with temporalchanges in an amount of absorbed X rays, that is, complex changes in CTvalues with time.

In the case where the similar case search system or the like describedin U.S. Patent Application Publication No. 20040003001 or JapaneseUnexamined Patent Publication No. 2004-173748 is applied toidentification of such a liver tumor, not all temporal change imagesdescribed above are used, since the system searches for similar cases byusing only one image as a search target.

Furthermore, the system does not maximally use information obtained inexaminations, and whether images to be compared to each other wereobtained at the same time phase has not been considered.

SUMMARY OF THE INVENTION

The present invention has been conceived based on consideration of theabove circumstances, and an object of the present invention is toprovide an apparatus, a method, and a recording medium storing a programthat can achieve higher accuracy in a search for a similar case in thecase where images at different time phases exist.

A similar case search apparatus of the present invention comprises:

a similar case database storing similar case information sets eachincluding: examination identification information that identifies anexamination for obtaining a medical image; time phase informationrepresenting each of time phases in the case where a plurality ofmedical images at the respective time phases are obtained in theexamination; characteristic information representing a content-basedcharacteristic of at least a region in the medical image; and imageinterpretation/diagnosis support information for supportinginterpretation of a medical image whose content-based characteristic issimilar thereto and/or for supporting diagnosis based on the medicalimage having the similar content-based characteristic, while relatingthe time phase information of each of the time phases to the examinationidentification information in each of the similar case information setsand relating the characteristic information in each of the similar caseinformation sets to the time phase information of each of the timephases;

time phase information acquisition means for obtaining informationrepresenting different time phases of a plurality of search targetimages obtained at the time phases in one and the same examination fromaccompanying information added to the respective search target images;and

similar case search means for carrying out a search of the similar casedatabase for at least the image interpretation/diagnosis supportinformation in a corresponding portion of the similar case informationsets that satisfies all of search conditions comprising: a first searchcondition that the time phase information representing the respectivetime phases of the search target images exists; a second searchcondition that the time phase information representing the respectivetime phases is related to the examination identification informationrepresenting one and the same examination; and a third search conditionthat the characteristic information related to the time phaseinformation representing each of the time phases represents similarityin the content-based characteristic to at least a region in acorresponding one of the search target images at the corresponding timephase.

A similar case search method of the present invention comprises thesteps of:

obtaining information representing different time phases of a pluralityof search target images obtained at the respective time phases in oneand the same examination from accompanying information added to therespective search target images; and

searching a similar case database storing similar case information setseach including: examination identification information that identifiesan examination for obtaining a medical image; time phase informationrepresenting each of time phases in the case where a plurality ofmedical images at the respective time phases are obtained in theexamination; characteristic information representing a content-basedcharacteristic of at least a region in the medical image; and imageinterpretation/diagnosis support information for supportinginterpretation of a medical image whose content-based characteristic issimilar thereto and/or for supporting diagnosis based on the medicalimage having the similar content-based characteristic while relating thetime phase information of each of the time phases to the examinationidentification information in each of the similar case information setsand relating the characteristic information in each of the similar caseinformation sets to the time phase information of each of the timephases. The step of searching is the step of searching the database forat least the image interpretation/diagnosis support information in acorresponding portion of the similar case information sets thatsatisfies all of search conditions comprising: a first search conditionthat the time phase information representing the respective time phasesof the search target images exists; a second search condition that thetime phase information representing the respective time phases isrelated to the examination identification information representing oneand the same examination; and a third search condition that thecharacteristic information related to the time phase informationrepresenting each of the time phases represents similarity in thecontent-based characteristic to at least a region in a corresponding oneof the search target images at the corresponding time phase.

A recording medium storing a similar case search program of the presentinvention stores a program that causes a computer to execute the methoddescribed above.

Hereinafter, the present invention will be described in detail.

The “examination” refers to imaging by one type of examination modality.

The “medical images” refer to images representing a predetermined bodypart of a subject as an examination target obtained by an examinationmodality such as CT or MRI. More specifically, the medical images referto slice images of abdomen (liver) of a human body obtained by CT.

The case where images representing temporal changes in an examinationtarget body part associated with infusion of a contrast material areobtained can be listed as an example of the case where “a plurality ofmedical images at the respective time phases were obtained in theexamination”. More specifically, the case refers to the case where fourimages are obtained representing a pre-contrast phase image, an earlyphase image, a portal phase image, and a late phase image in anexamination of liver tumor, for example.

The “time phase information” refers to each of stages of temporalchanges, such as a pre-contrast phase, an early phase, a portal phase,and a late phase. Description of series as a portion of the accompanyinginformation of the medical images may be used as the time phaseinformation. Alternatively, in the case where the time elapsed afterinfusion of a contrast material is added to the images, the time phasesmay be assigned to the images based on the elapsed time.

A region of interest is listed as “at least a region in the medicalimage”. The region of interest is a region to which attention is paid atthe time of image interpretation and diagnosis, and a characteristicthereof greatly affects diagnosis. The region of interest is generallyreferred to as ROI (Region Of Interest). The region of interest may be aregion specified by an observer of the medical image displayed on ascreen with a pointing device or the like, or detected by a known imageanalysis method for detecting a region of abnormal shadow in a medicalimage. Alternatively, the region of interest maybe a region determinedby combination of manual specification and detection, such as a regionspecified by the observer and an outline of which is extracted by thedetection method, or a region detected by the method and selected by theobserver. The region of interest in a second search target image that isdifferent from a first search target image may be automaticallydetermined at a position corresponding to the region of interestdetermined in the first search target image.

The “content-based characteristic” refers to a characteristic related tothe content of the medical image. More specifically, the content-basedcharacteristic refers to a characteristic of luminance, an edge, ashape, a size, or an isolated region, for example. The content-basedcharacteristic may be a combination of a plurality of types ofcharacteristics.

“Representing a content-based characteristic of at least a region in themedical image” refers to a content-based characteristic of the regionsuch as a region of interest in the medical image, or a content-basedcharacteristic of the entire image, or a content-based characteristic ofthe region and of the entire image, or a combination of a content-basedcharacteristic of the region and a content-based characteristic of aremaining region.

A characteristic quantity that quantifies the content-basedcharacteristic maybe an example of the “characteristic information”. Thecharacteristic quantity can be obtained by a known image analysismethod. The characteristic information may be image data themselves.

An image interpretation report of the medical image generated by aradiologist or the like or finally confirmed diagnosis information onthe examination target body part in the medical image may be listed asan example of the “image interpretation/diagnosis support information”.Alternatively, the image interpretation/diagnosis support informationmay be the medical image itself representing the examination target bodypart. Hereinafter, each of the examples will be described below indetail.

The image interpretation report or the finally confirmed diagnosisinformation maybe generated based on image interpretation informationand/or diagnosis information obtained from storage means that stores theimage interpretation information representing a result of imageinterpretation of the medical image of the subject and/or the diagnosisinformation representing the content of diagnosis of the subject whilerelating the image interpretation information and/or the diagnosisinformation to the medical image of the subject.

A database that stores image interpretation reports, electronic charts,and the like and comprises a medical information management system suchas a Radiology Information System (RIS), a Picture Archive andCommunication System (PACS), or a Hospital Information System (HIS) maybe listed as an example of the storage means.

Storing the image interpretation information and/or the diagnosisinformation by relating the image interpretation information and/or thediagnosis information to the medical image refers to storing the imageinterpretation information and/or the diagnosis information in a statewhere a portion of either the image interpretation information and/orthe diagnosis information or the medical image allows direct or indirectaccess to the other. As an example of direct access, the case may belisted where the image interpretation information has a report ID thatidentifies the image interpretation information itself and an image IDthat identifies the medical image having been interpreted while themedical image has the image ID that identifies the image itself and thereport ID that identifies the image interpretation report of the image.In this case, the image interpretation information allows direct accessto the medical image based on the image ID while the medical imageallows direct access to the image interpretation information based onthe report ID. As an example of indirect access, the following case maybe listed. The diagnosis information has a examination ID thatidentifies the diagnosis information and an examination ID thatidentifies an examination carried out on the patient while the medicalimage has an image ID that identifies the image itself and theexamination ID that identifies the examination including imaging of themedical image. In addition, examination information including theexamination ID that identifies the examination, the examination ID thatidentifies the patient having been subjected to the examination, and theimage ID that identifies the image obtained in the examination exists.In this case, the diagnosis information allows indirect access to themedical image by identifying the examination information according tothe examination ID and by identifying the image obtained in theexamination according to the image ID included in the examinationinformation. The medical image also allows indirect access to thediagnosis information by identifying the examination informationaccording to the examination ID and by identifying the diagnosisinformation based on the examination ID included in the examinationinformation.

The “storage means” does not need to store the medical image related tothe image interpretation information and/or the diagnosis information.

The “image interpretation information” may be an image interpretationreport describing an image interpretation result by a plurality ofradiologists. The “diagnosis information” can include not only thefinally confirmed diagnosis information and a remark based on thecorresponding medical image but also all information that can beobtained during a diagnosis process of the subject, such as a result ofanother examination or health interview, and the content of treatment.

The image interpretation/diagnosis support information may be generatedbased on the image interpretation information and/or the diagnosisinformation by extraction of predetermined information from the imageinterpretation information and/or the diagnosis information or by usingthe image interpretation information and/or the diagnosis information asthe image interpretation/diagnosis support information.

The “image interpretation/diagnosis support information” may be linkinformation to a location of storage of the content thereof. Morespecifically, the image interpretation/diagnosis support information maybe the name of a database that stores the image interpretation report ofthe medical image, an electronic chart of the subject, and the medicalimage itself, and search key information for obtaining information fromthe database.

The “examination identification information” and the “time phaseinformation” included in each of the similar case information sets inthe similar case database may be defined as items of the database (atable). Alternatively, like the search target images, the examinationidentification information and the time phase information may be aportion of the “characteristic information” or the “imageinterpretation/diagnosis support information”, attached to the medicalimages stored in the database. The method by which the examinationidentification information and the time phase information are attachedto the medical images is the same as that for the search target images.

As a method of adding the “accompanying information” to the medicalimage, a method according to the DICOM standard may be listed. In theDICOM standard, the “examination identification information” is added asgeneral examination information, and the “time phase information” isadded as a series description, positional relation information inseries, or contrast material information, for example.

As an example of judgment according to the “third search condition” asto whether “the characteristic information related to the time phaseinformation representing each of the time phases represents similarityin the content-based characteristic to at least a region in acorresponding one of the search target images at the corresponding timephase”, judgment processing according to a criterion may be used. Thecriterion may be that a difference of the characteristic quantity in atleast a region in the search target image from the characteristicinformation (the characteristic quantity) in the corresponding similarcase information set is minimal, or a predetermined threshold value orsmaller. Alternatively, the criterion may be that up to a predeterminednumber of the similar case information sets are extracted in order ofsmaller difference of the characteristic quantity, for example.

As a specific method of the search according to the first to thirdsearch conditions, the following method may be used. The methodcomprises the steps of:

obtaining a corresponding portion of the similar case information setshaving the time phase information representing the time phase of a firstsearch target image as one of the search target images and representingthat the characteristic information related to the time phaseinformation thereof shows similarity in the content-based characteristicto at least a region in the first search target image; and

extracting a corresponding portion of the similar case information setshaving the time phase information representing the time phase of asecond search target image different from the first search target imageand showing similarity in the content-based characteristic in thecharacteristic information related to the time phase information to atleast a region in the second search target image, from a correspondingportion of the similar case information sets having the examinationidentification information representing the same examination as theportion of the similar case information sets having been obtained.

When judgment is made on the similarity of the content-basedcharacteristic to at least a region in the second search target image, acorresponding portion of the similar case information sets representingthat a difference in the characteristic information between therespective time phases thereof is similar to a difference in thecontent-based characteristic of at least a region between the first andsecond search target images may be extracted from within a correspondingportion of the similar case information sets having the examinationidentification information representing the same examination and havingthe time phase information representing the time phases of the first andsecond search target images. In this case, the difference in thecontent-based characteristic between the medical images at the differenttime phases in one and the same examination may have been registered asthe characteristic information of a corresponding portion of the similarcase information sets in the similar case database.

Upon judgment on a degree of conformity with the first to third searchconditions described above, the degree of conformity may be lowered inthe following order:

(1) the case where a corresponding portion of the similar caseinformation sets satisfying all the first to third search conditionsexists for all the search target images;

(2) the case where a corresponding portion of the similar caseinformation sets satisfying all the first to third search conditionsexists for a portion of the search target images but a correspondingportion of the similar case information sets satisfying the first orsecond search condition does not exist for the remaining portion of thesearch target images;

(3) the case where a corresponding portion of the similar caseinformation sets satisfying all the first to third search conditionsexists for a portion of the search target images but a correspondingportion of the similar case information sets satisfying the third searchcondition does not exist for the remaining portion of the search targetimages although a corresponding portion of the similar case informationsets satisfying the first or second search condition exists for theremaining portion of the search target images.

Moreover, examination identification information that identifies theexamination in which the first search target image as one of the searchtarget images was obtained and the information representing the timephase of the first search target image may be obtained from theaccompanying information of the first search target image so that amedical image having the accompanying information including theexamination identification information representing that the medicalimage was obtained in the same examination as the first search targetimage and including the information representing the time phasedifferent from the first search target image can be obtained as thesecond search target image.

The similar case search apparatus of the present invention may furthercomprise means for outputting the portion of the similar caseinformation sets having been obtained in the search. More specifically,the portion of the similar case information sets may be outputted asdisplay on a display screen, or by printing, or as electronic data in arecording medium of the search apparatus. The content of the output maybe all the portion of the similar case information sets, or a portionthereof. Alternatively, in the case where the portion of the similarcase information sets was not found through the search, the content ofthe output may be information representing the fact.

By execution of the similar case search of the present invention, thetime phase information of each of the search target images obtained atthe respective time phases in the same examination is obtained from theaccompanying information of the images. The similar case databasestoring the similar case information sets each having the examinationidentification information, the time phase information, thecharacteristic information, and the image interpretation/diagnosissupport information is then searched for the portion of the similar caseinformation sets satisfying all the search conditions comprising thefirst search condition that the time phase information representing thetime phases of the search target images exists, the second searchcondition that the time phase information representing the time phasesof the search target images is related to the examination identificationinformation representing one and the same examination, and the thirdsearch condition that the characteristic information related to the timephase information representing the time phases shows similarity in thecontent-based characteristic to at least a region in the search targetimages of the corresponding time phases. In other words, the similarcase database is searched by using the images obtained at the differenttime phases in the same examination as the search target images, and theportion of the similar case information sets satisfying the three searchconditions, that is, agreement of the time phases to the search targetimages, agreement of the examination therein, and similarity in thecontent-based characteristic to the search target images is obtained.Therefore, by effectively using the images at the different time phasesin the same examination, which have not been used conventionally,accuracy improves in the similar case search. Consequently, thisimprovement contributes to reduction in errors in judgment at the timeof image interpretation or diagnosis, such as erroneous judgment causedby incapability to detect a difference between veins and a lesion.

In the case where the search according to the first to third searchconditions comprises the steps of: obtaining the portion of the similarcase information sets whose time phase information is the same as thefirst search target image and whose characteristic information relatedto the time phase information representing the time phase is similar inthe content-based characteristic to at least a region in the firstsearch target image; and extracting the portion of the similar caseinformation sets whose time phase information is the same as the secondsearch target image and whose characteristic information related to thetime phase information representing the time phase is similar in thecontent-based characteristic to at least a region in the second searchtarget image from the portion of the similar case information setshaving the same examination identification information as the portion ofthe similar case information sets having been obtained, a portion of thesimilar case information sets whose similarity in the content-basedcharacteristic to the second search target image is judged is limited toa corresponding portion of the similar case information sets obtained inthe same examination as the portion of the similar case information setssatisfying the conditions of agreement of the time phase and similarityin the content-based characteristic to the first search target image.Therefore, the number of times of processing to judge the similarity inthe content-based characteristic, which imposes a heavy processing load,can be reduced. Consequently, the search processing can be faster.

Upon judgment on the similarity in the content-based characteristic toat least a region in the second search target image, in the case wherethe portion of the similar case information sets showing similarity inthe difference of the characteristic information between the time phasesthereof to the difference in the content-based characteristic of atleast a region between the first and second search target images isextracted from within the portion of the similar case information setshaving the examination identification information representing the sameexamination and having the same time phases as the first and secondsearch target images, the similarity can be judged while reflecting achange between the corresponding medical images at the respective timephases. Consequently, accuracy of the search improves.

Upon judgment on the degree of conformity with the first to third searchconditions described above, if the degree of conformity is lowered forthe case where the portion of the similar case information setssatisfying all the first to third search conditions exists for a portionof the search target images although the portion of the similar caseinformation sets satisfying the third search condition does not existfor the remaining portion of the search target images regardless ofexistence of the portion of the similar case information sets satisfyingthe first or second search condition for the remaining portion of thesearch target images than for the case where the corresponding portionof the similar case information sets satisfying all the first to thirdsearch conditions exists for a portion of the search target imagesalthough the corresponding portion of the similar case information setssatisfying the first or second search condition does not exist for theremaining portion of the search target images, distinction can be madebetween the case where the portion of the similar case information setscorresponding to the respective time phases of the search target imagesexists but the content-based characteristic thereof is dissimilar for aportion of the corresponding medical images and the case where a portionof the similar case information sets corresponding to a portion of thetime phases of the search target images does not exist. Therefore, thedegree of conformity for the former case that is not thought to besimilar cases when the time elapsed in the examination is considered canbe lowered than for the latter case where pictorial similarity deservesconsideration although the time elapsed in the examination cannot beconsidered. Consequently, the more detailed similar case informationsets can be provided.

If the examination identification information and the time phaseinformation is obtained from the accompanying information of the firstsearch target image and if the second search target image generated inthe same examination as the first search target image but having adifferent time phase from the first search target image is obtainedbased on the examination identification information and the time phaseinformation having been obtained, similar cases including the secondsearch target image can be searched for even in the case where a medicalimage observer recognizes only the first search target image.Consequently, accuracy of image interpretation and diagnosis can beimproved.

In the case where the characteristic quantity representing thecontent-based characteristic of at least a region in the correspondingmedical image is registered as the characteristic information in theeach of the similar case information sets instead of the medical imageitself, the characteristic quantity does not need to be calculated fromthe image data registered as the characteristic information, in eachsearch for similar cases. Consequently, a processing load can bereduced.

If a target of judgment on the similarity of the content-basedcharacteristic is a region of interest in the corresponding medicalimage, more appropriate similar cases can be searched for by judgment onthe similarity of the content-based characteristic in the important partof the image. Therefore, accuracy of image interpretation/diagnosisimproves. If the region of interest in the second search target image isautomatically set at the position corresponding to the region ofinterest in the first search target image, an image interpreter/a personwho diagnoses does not need to set the region of interest therein. Ifthe region of interest is detected automatically in each of the searchtarget images, a burden on the interpreter/the person who diagnoses canbe reduced further, and oversight of a lesion in the correspondingmedical image is reduced.

If the image interpretation/diagnosis support information includes thecorresponding medical image itself that is related thereto, the medicalimage obtained as the image interpretation/diagnosis support informationcan be referred to upon image interpretation of the search target imagesand upon diagnosis based on the search target images, which contributesto comparison and interpretation of the images.

In the case where the image interpretation/diagnosis support informationis the link information to the image interpretation/diagnosis supportinformation and to the image data stored in another medical informationsystem such as RIS, PACS, or HIS, storage space can be saved, since theinformation of the same content does not need to be stored at aplurality of locations. In addition, disagreement in data content thatcould occur in the case where only the information stored at one of thelocations has been updated can be avoided, and reliability of theinformation improves. Furthermore, simultaneous processing of the datato avoid such disagreement becomes unnecessary. In this manner, aprocessing load on the system can be reduced. The effect of avoidance ofthe data disagreement problem is high, since electronic chartinformation or the like as an example of the diagnosis information is tobe updated especially.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of a medical information system to whicha similar case search apparatus of an embodiment of the presentinvention has been introduced;

FIG. 2 is a block diagram showing the configuration of the similar casesearch apparatus in the embodiment;

FIGS. 3A and 3B show examples of a similar case database in theembodiment;

FIG. 4 is a flow chart showing procedures of similar case searchprocessing in the embodiment;

FIGS. 5A and 5B show examples of medical images at different contrastenhancement phases to be interpreted and used as search target images;

FIG. 6 is a block diagram showing an example of processing to judge adegree of conformity with search conditions;

FIG. 7 is a block diagram showing the configuration of a similar casesearch apparatus as a modification to the embodiment; and

FIG. 8 shows an example of an index table for the similar case databasein the embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, an embodiment of the present invention will be describedwith reference to the accompanying drawings.

FIG. 1 shows the configuration of a medical information system to whicha similar case search apparatus of a first embodiment of the presentinvention has been introduced. As shown in FIG. 1, the system comprisesan imaging apparatus (a modality) 1 for obtaining medical images, aworkstation (QA-WS) 2 for checking image quality, workstations 3 (3 aand 3 b) for physicians to perform imaging diagnosis (hereinafter simplyreferred to as the workstations 3), an image information managementserver 4, an image information database 5, an image interpretationreport server 6, an image interpretation report database 7, a similarcase search server 8, and a similar case database 9, all of which areconnected in a communicable state via a network 19. Each of theapparatuses is controlled by a program installed from a recording mediumsuch as a CD-ROM. The program may be installed after being downloadedfrom a server connected via a network such as the Internet.

The modality 1 includes an apparatus that generates an image data setrepresenting a three-dimensional image of a body part of a subject byimaging the body part as an examination target. The modality 1 outputsthe image data set added with accompanying information defined by theDICOM standard, as an image information set. More specifically, themodality 1 may be an apparatus of CT (Computed Tomography), MRI(Magnetic Resonance Imaging), PET (Positron Emission Tomography), orultrasonography. The modality 1 also obtains images of temporal changesin the examination target body part associated with infusion of acontrast material, by CT or the like. The images can be search targetimages for the similar case search apparatus of the present invention.Hereinafter, the “image information set” refers to a combination of theimage data set representing the subject and the accompanying informationadded thereto. In other words, the image information set includes textinformation regarding the medical image.

The QA-WS 2 comprises a general-purpose processor (a computer), one ortwo high-definition display(s), and input devices such as a mouse and akeyboard. Software, for supporting operation by a technician who is toperform examinations, is installed in the processor. According to afunction realized by execution of the software, the QA-WS 2 receives theimage information set according to the DICOM standard from the modality1, and prompts the technologist to confirm the image data set includedin the image information set and the content of the accompanyinginformation therein by display of the image information set on a screen.The QA-WS 2 transfers the image information set confirmed by thetechnologist to the image information management server 4 via thenetwork 19, and requests registration of the image information set withthe image information database 5.

The workstations 3 are apparatuses for physicians to perform imagingdiagnosis and used by the physicians to interpret the medical images andto generate image interpretation reports. Each of the workstations 3comprises a processor, one or two high-definition display(s)(hereinafter, the display or one of the displays is referred to as thedisplay), and input devices such as a mouse and a keyboard. Theworkstations 3 request image viewing from the image informationmanagement server 4, display the images received from the imageinformation management server 4, automatically detect parts in theimages which seem to be lesions and display the parts with emphasisthereon, support generation of the image interpretation reports, requestregistration and viewing of the image interpretation reports from theimage interpretation report server 6, display the image interpretationreports received from the image interpretation report server 6, requestviewing of similar case information sets from the similar case searchserver 8, display the similar case information sets received from thesimilar case search server 8, and request registration of similar caseinformation sets from the similar case search server 8, for example.

The image information management server 4 is a general-purpose computerwith comparatively high performance, and has a software programinstalled therein for providing functions of a database managementsystem (DBMS). The image information management server 4 also has alarge-capacity storage comprising the image information database 5. Thestorage may be a large-capacity hard disk connected to the imageinformation management server 4 by a data bus, or a disk deviceconnected to a NAS (Network Attached Storage) or SAN (Storage AreaNetwork) connected to the network 19.

Image data sets representing images of subjects and accompanyinginformation thereof are registered with the image information database5. The accompanying information can include image ID for identifyingeach of the images, examination ID for identifying each of the subjects,examination ID for identifying an examination, unique identifier (UID)assigned for each of the image information sets, date of examination onwhich the corresponding image information set was generated, time of theexamination, type of modality used in the examination for obtaining theimage information set, patient information such as name, age, and genderof patient, examined body part (imaged body part), imaging condition(use or non-use of contrast material and time elapsed after infusion ofthe material/dye used in imaging, type of radionuclide, amount ofradionuclide, and so on), and series number or collection number when aplurality of images were obtained in one examination, for example. Theimage information sets are managed as XML or GML data.

When the image information management server 4 receives a request forregistration of the image information set sent from the QA-WS 2, theimage information management server 4 changes the image information setinto the format for the image information database, and registers theimage information set with the image information database 5.

Upon reception of viewing request sent from any one of the workstations3 (hereinafter referred to as the workstation 3) via the network 19, theimage information management server 4 searches the image informationsets registered with the image information database 5, and extracts arequested one of the image information sets to send the imageinformation set to the workstation 3.

When a user such as a physician to carry out imaging diagnosis operatesthe workstation 3 to request viewing of one or more of the images as atarget of image interpretation (hereinafter referred to as the imageinterpretation target image or images), the workstation 3 sends aviewing request to the image information management server 4, andobtains the corresponding image information set or sets necessary forimage interpretation. The workstation 3 displays the image informationset or sets on a display screen, and carries out automatic lesiondetection processing or the like in response to a request of thephysician.

The workstation 3 further displays a report generating screen on thedisplay screen for supporting generation of a corresponding imageinterpretation report. When a radiologist inputs text representing adiagnosis (a remark and the like) based on image interpretation, theworkstation 3 generates the image interpretation report that records theinputted information and the interpretation target image or images. Whenthe number of the image interpretation target images is larger than 1,the image interpretation report records a representative one of theimages (hereinafter referred to as the representative image) thatinfluenced the diagnosis most. The workstation 3 transfers the generatedimage interpretation report to the image interpretation report server 6via the network 19, and requests registration of the report with theimage interpretation report database 7.

The image interpretation report server 6 is a general-purpose computerwith comparatively high performance, and has a software programinstalled therein to provide functions of a database management system(DBMS). Upon reception of the request for registration of the imageinterpretation report sent from the workstation 3, the imageinterpretation report server 6 changes the image interpretation reportinto the format to fit the database, and registers the report with theimage interpretation report database 7.

Information such as image ID for identifying the image interpretationtarget image or the representative image, image interpreter ID foridentifying the physician who carried out image interpretation, positioninformation on region of interest, remark, and certainty of the remarkis registered with the image interpretation report database 7. Inaddition, the image interpretation report database 7 can also includeexamination number and patient number obtained by referring to theaccompanying information of the image information set at the time ofimage interpretation, and an image data set itself of the imageinterpretation target image or the representative image. The image dataset may be a copy of the image data set registered with the imageinformation database, or a reduced image data set having a smallernumber of pixels (that is, thinned data) than the image data set in theimage information database 5. The image data set may be link informationrepresenting location (such as a folder) and file name of the image dataset in the image information database 5, for example. The positioninformation on the region of interest may be registered with the imageinformation database 5 as a portion of the accompanying information ofthe image data set, instead of the image interpretation report database7. The image interpretation report is managed as XML or GML data, forexample.

Upon reception of a viewing request sent from the workstation 3 via thenetwork 19, the image interpretation report server 6 searches the imageinterpretation reports registered with the image interpretation reportdatabase 7, and sends an extracted one of the reports to the workstation3 requesting the report.

The similar case search server 8 is a general-purpose computer withcomparatively high performance, and has a software program installedtherein to provide functions of database management system (DBMS). Thesimilar case database 9 stores the images having been interpreted andimage interpretation results on the images, as the similar caseinformation sets. The similar case search apparatus as the embodiment ofthe present invention is installed as a client-server system wherein thesimilar case search server 8 having the similar case database 9 isconnected with the workstations 3 by the network 19. Details of theapparatus will be described later.

The network 19 is a local area network connecting various kinds ofapparatuses in a hospital. In the case where a part of the workstations3 is also installed in another hospital or clinic, the network 19 mayconnect local area networks in the respective hospitals by the Internetor a dedicated line. In either case, it is preferable for the network 19to be an optical network or the like that can realize high-speedtransfer of the image information sets.

The similar case search apparatus in the embodiment of the presentinvention will be described below in detail for the case as an examplewhere the interpretation target images are four images obtained by CTand representing temporal changes in a liver associated with infusion ofa contrast material. The four images represent four contrast enhancementphases (time phases), that is, at a pre-contrast phase (plain CT), anearly phase (an arterial phase), a portal phase (a portal venous phase),and a late phase (an equilibrium phase). FIG. 2 is a block diagramshowing the configuration of the similar case search apparatus and theflow of data therein. As shown in FIG. 2, the apparatus comprises acontrast enhancement information analysis unit 21, a unit 22 for settinga region of interest (hereinafter referred to as the ROI setting unit22), a unit 23 for reflecting the region of interest (hereinafterreferred to as the ROI reflecting unit 23), a characteristic quantitycalculation unit 24, a first similar case information search unit 25, asecond similar case information search unit 26, a judgment unit 27, andthe similar case database 9.

The contrast enhancement information analysis unit 21 analyses seriesdescription, positional relationship information on series, and contrastmaterial information as a portion of the accompanying information ofeach of the image data sets conformed to the DICOM standard having beeninputted, and obtains contrast enhancement information representing anyone of the four contrast enhancement phases described above. Thecontrast enhancement information analysis unit 21 stores the contrastenhancement information in a memory of the workstation 3.

The ROI setting unit 22 receives setting of the region of interestinputted through operation of one of the input devices such as themouse, in the image displayed in a predetermined area of the display ofthe workstation 3 (hereinafter referred to as the first search targetimage), and finds the position information on the region of interest anda portion of the image information set corresponding to the region, inorder to store the position information and the portion of the imageinformation set in the memory of the workstation 3.

Using the position information on the region of interest and the imagedata set of a second search target image inputted thereto, the ROIreflecting unit 23 sets a region of interest at the inputted position inthe inputted image data set of the second search target image, and findsthe position information on the region of interest having been set and aportion of the image information set corresponding to the region, inorder to store the position information and the portion of the imageinformation set in the memory of the workstation 3.

The characteristic quantity calculation unit 24 carries out imageanalysis processing on the inputted image data sets (the portions of theimage information sets corresponding to the region of interest) of thefirst and second search target images, and calculates a characteristicquantity thereof. Examples of the characteristic quantity include aposition and a size (diameter) of an abnormal shadow in the region ofinterest, a luminance histogram thereof, and shape information andtexture information of a lesion in the region of interest obtained by anAAM (Active Appearance Models) method (T. F. Cootes et al., “ActiveAppearance Models”, Proc. 5_(th) European Conference on Computer Vision,vol. 2, pp. 484-498, Springer, 1998). The characteristic quantity may bea combination of a plurality of types of characteristic quantities.

Using the contrast enhancement information and information on thecharacteristic quantity of the first search target image inputtedthereto, the first similar case information search unit 25 obtains acorresponding portion of the similar case information sets whosecontrast enhancement information agrees with the inputted contrastenhancement information and whose characteristic quantity is differentfrom the inputted characteristic quantity by a predetermined thresholdvalue or smaller, from the similar case database 9.

Using the portion of the similar case information sets obtained by thefirst similar case information search unit 25 and the contrastenhancement information of the second search target image inputtedthereto, the second similar case information search unit 26 obtains acorresponding portion of the similar case information sets whoseexamination ID is the same as the inputted similar case information setsand whose contrast enhancement information agrees with the inputtedcontrast enhancement information, from the similar case database 9.

Using the portion of the similar case information sets (hereinafterreferred to as the similar case information sets A) obtained by thefirst similar case information search unit 25, the portion of thesimilar case information sets (hereinafter referred to as the similarcase information sets B) obtained by the second similar case informationsearch unit 25, and the characteristic quantity of the region ofinterest in the second search target image inputted thereto, thejudgment unit 27 judges a degree of conformity of each of the similarcase information sets with search conditions. More specifically, thejudgment unit 27 judges that a portion of the similar case informationsets B has a highest degree of conformity if the portion has thecharacteristic quantity whose difference from the characteristicquantity in the region of interest in the second search target image isa predetermined threshold value or smaller, that is, if the portion isthe similar case information sets representing appropriate similar casesto both the first and second search target images. The judgment unit 27then judges that a portion of the similar case information sets A fromwhich the similar case information sets B have not been obtained, thatis, the similar case information sets representing cases only similar tothe first search target image has a second highest degree of conformity.The judgment unit 27 judges that a portion of the similar caseinformation sets B has a lowest degree of conformity if the portion hasthe characteristic quantity whose difference from the characteristicquantity in the region of interest in the second search target image islarger than the predetermined threshold value, that is, if the portionis the similar case information sets that represent similar cases to thefirst search target image but do not represent appropriate similar casesto the second search target image at the same contrast enhancement phaseas the second search target image in the examinations in which thesimilar case information sets representing the similar cases to thefirst search target image were obtained.

FIGS. 3A and 3B show examples of the configuration of the database 9.The similar case database 9 stores the similar case information setseach including the examination ID that identifies the examination inwhich the corresponding medical image that can be a similar case imagewas obtained, the contrast enhancement information (contrast enhancementphases) of the image, the characteristic quantity of the region ofinterest in the image, and the image interpretation/diagnosis supportinformation including the image interpretation result on the image andfinally confirmed diagnosis information based on the image.

In the example shown in FIG. 3A, the similar case database 9 comprises acharacteristic quantity table 9 a storing the characteristic quantitycorresponding to each of the examination IDs and to the contrastenhancement information representing each of the phases and an imageinterpretation/diagnosis support information table 9 b storing the imageinterpretation/diagnosis support information corresponding to each ofthe examination IDs. The tables 9 a and 9 b are related to each other bythe examination IDs. This structure can be preferably adopted for thecase where the images that can represent similar cases exist for each ofthe contrast enhancement phases but the image interpretation/diagnosissupport information exists for each of the examinations.

In the example shown in FIG. 3B, the similar case database 9 comprisesonly a similar case information table 9 c storing the characteristicquantity of the region of interest in each of the images that canrepresent a similar case and the image interpretation/diagnosis supportinformation, for each of the examination IDs and the contrastenhancement information representing each of the phases. This structureis preferably adopted for the case where the imageinterpretation/diagnosis support information exists for each of theimages that can represent a similar case. More specifically, the caserefers to the case where the image itself that can represent a similarcase is registered as a portion of the image interpretation/diagnosissupport information.

Each of the processing units is appropriately distributed according tovarious performance requisites such as performance of the workstations3, the similar case search server 8, and the network 19, the number ofthe workstations 3, frequency of access to the similar case searchserver 8, and response time. For example, the contrast enhancementinformation analysis unit 21, the ROI setting unit 22, the ROIreflecting unit 23, the characteristic quantity calculation unit 24, andthe judgment unit 27 may be installed in each of the workstations 3while the first similar case information search unit 25 and the secondsimilar case information search unit 26 may be installed in the similarcase search server 8. Alternatively, the contrast enhancementinformation analysis unit 21, the ROI setting unit 22, the ROIreflecting unit 23, and the judgment unit 27 may be installed in each ofthe workstations 3 while the characteristic quantity calculation unit24, the first similar case information search unit 25, and the secondsimilar case information search unit 26 maybe installed in the similarcase search server 8.

Procedures of the similar case search processing will be described belowin detail by use of the flow chart in FIG. 4, the data flow in the blockdiagram in FIG. 2, and the database structures shown in FIGS. 3A and 3B.

User authentication of a physician to perform imaging diagnosis iscarried out on the workstation 3 according to user ID and password, orbiometric information such as a fingerprint, to access the medicalinformation system. After the user authentication has been successfullycarried out, an examination (interpretation) target image list isdisplayed on the display based on an imaging diagnosis order issued byan ordering system. The physician selects interpretation target imagesI₁ and I₂ from the image list by use of any one of the input devicessuch as the mouse. Let the image I₁ and the image I₂ be an early phaseimage obtained by CT by the modality 1 with infusion of a contrastmaterial to a patient and a pre-contrast phase image obtained in thesame examination, respectively. The workstation 3 requests viewing fromthe image information management server 4 by using the image IDs of theselected images I₁ and I₂ as search keys. The image informationmanagement server 4 having received the request searches the imageinformation database 5 for image files (also referred to as I₁ and I₂for the sake of simpler description) of the interpretation target imagesI₁ and I₂. The image information management server 4 sends the imagefiles I₁ and I₂ to the workstation 3 that sent the request. Theworkstation 3 receives the image files I₁ and I₂ (#1).

The contrast enhancement information analysis unit 21 analyses theaccompanying information of the image files I₁ and I₂, and obtainscontrast enhancement information P_(a) and P_(b) of the respectiveimages (#2).

The workstation 3 displays the images I₁ and I₂ on the display based onthe image data sets of the image files I₁ and I₂, and also displays thecontrast enhancement information P_(a) and P_(b) obtained by thecontrast enhancement information analysis unit 21 at positions that canbe related to the images I₁ and I₂ (#3). FIG. 5A shows an example ofdisplay of the image I₁ while FIG. 5B shows an example of display of theimage I₂. Although not shown, the contrast enhancement information P_(a)and P_(b) (early phase and pre-contrast phase) is also displayed at thebottom of the corresponding images, for example.

The physician observes the images I₁ and I₂ displayed on the display. Inthe case where the physician has found a region (a cross-hatched area inFIG. 5A) that is suspicious to be a tumor in the center left of theimage I₁, the physician marks the region by use of the mouse or thelike. The ROI setting unit 22 identifies the position information andthe corresponding portion of the image information set of the regionmarked by the operation of the mouse or the like, and stores theposition information and the portion of the information set as aninformation set R₁ on the region of interest (hereinafter referred to asthe ROI information) in the memory of the workstation 3 (#4).

When the physician selects “similar case search” by menu selection froma user interface displayed on the display with the mouse or the like,the workstation 3 detects the selected event corresponding to the“similar case search” item in the menu (#5; YES), and carries out thesimilar case search processing that will be described later. In the casewhere another one of items has been selected, the selected processing iscarried out (#5; NO).

In the case where the “similar case search” has been selected (#5; YES),the characteristic quantity calculation unit 24 carries out the imageanalysis processing based on the ROI information R₁, and calculates acharacteristic quantity C₁ (#8).

The first similar case information search unit 25 searches the similarcase database 9 by using the calculated characteristic quantity C₁ andthe contrast enhancement information P_(a) as search keys, and obtainssimilar case information sets A₁, A₂, A₃, and A₄ at the same contrastenhancement phase as the image I₁ and having a content-basedcharacteristic similar to the ROI information R₁ of the image I₁ (#9,#10; YES).

More specifically, in the case where the similar case database 9 has thestructure shown in FIG. 3A, for example, the first similar caseinformation search unit 25 accesses the characteristic quantity table 9a and sequentially compares the contrast enhancement information of eachof records in the table 9 a with the contrast enhancement informationP_(a). In the case where the both agree, the first similar caseinformation search unit 25 obtains the characteristic quantity of thecorresponding record. The similar case information search unit 25 thenfinds the difference between the characteristic quantity C₁ and thecharacteristic quantity of the record. In the case where the differenceis the predetermined threshold value or smaller, the first similar caseinformation search unit 25 judges that the region of interest of theimage I₁ is similar to the region of interest in the image correspondingto the similar case information set, and accesses the imageinterpretation/diagnosis support information table 9 b by using theexamination ID of the record as a search key. The first similar caseinformation search unit 25 obtains the image interpretation/diagnosissupport information related to the examination ID. In this manner, thesimilar case information sets A1, A2, A3, and A4 each including at leastthe examination ID and the image interpretation/diagnosis supportinformation and preferably including the characteristic quantity can beobtained.

In the case where no records having the same contrast enhancementinformation as the image I₁ have been found in the characteristicquantity table 9 a or in the case where the records having the samecontrast enhancement information as the image I₁ exist in the table 9 abut the difference between the characteristic quantity C₁ and thecharacteristic quantity of each of the records is larger than thepredetermined threshold value, the first similar case information searchunit 25 judges that no similar case information sets corresponding tothe image I₁ exist in the similar case database 9 (#10; NO), anddisplays a message “NO SIMILAR CASES” on the display of the workstation3 (#14).

The second similar case information search unit 26 obtains theexamination IDs of the similar case information sets A₁ to A₄, andobtains similar case information sets B₁ and B₂ having the sameexamination IDs as the examination IDs of the similar case informationsets A₁ to A₄ and having the same contrast enhancement information asthe contrast enhancement information P_(b) of the image I₂ from thesimilar case database 9 (#11).

More specifically, in the case where the similar case database 9 has thestructure shown in FIG. 3A, the second similar case information searchunit 26 accesses the characteristic quantity table 9 a, and sequentiallycompares each of the examination IDs of the similar case informationsets A₁ to A₄ with the examination ID of each of the records in thetable 9 a. In the case where the both agree, the second similar caseinformation search unit 26 compares the contrast enhancement informationP_(b) with the contrast enhancement information in the table. In thecase where the both agree, the second similar case information searchunit 26 obtains the characteristic quantity of the record, and accessesthe image interpretation/diagnosis support information table 9 b byusing the examination ID of the record as a search key. The secondsimilar case information search unit 26 then obtains the imageinterpretation/diagnosis support information related to the examinationID. In this manner, the second similar case information search unit 26obtains the similar case information sets B₁ and B₂ having at least thecharacteristic quantity and the image interpretation/diagnosis supportinformation. In this example, assume that the similar case informationsets A₁ and B₁ have the same examination ID while the similar caseinformation sets A₂ and B₂ have the same examination ID. For the similarcase information set A₃, a corresponding portion of the similar caseinformation sets having the same the examination ID exists but nosimilar case information sets having the same contrast enhancement phaseas the image I₂ (that is, the same contrast enhancement information asthe contrast enhancement information P_(b)) have been found therefrom.For the similar case information set A₄, no similar case informationsets having the same examination ID exist. Information representing thatno similar case information sets having the same contrast enhancementinformation as the similar case information set A₃ exist and informationrepresenting that no similar case information sets having the sameexamination ID as the similar case information set A₄ exist is coded andstored in a memory, for example, and usable by the judgment unit 27 aswill be described later.

In parallel to Steps #8 to #11 described above, the ROI reflecting unit23 sets the region of interest (a region in a broken circle in FIG. 5B)at the position in the image I₂ corresponding to the region of interestR₁, by using the position information of the region of interest and theimage data set of the image I₂. The ROI reflecting unit 23 stores theposition information and the corresponding portion of the imageinformation set as ROI information R₂ in the memory of the workstation 3(#6).

The characteristic quantity calculation unit 24 then carries out theimage analysis processing based on the ROI information R₂, andcalculates a characteristic quantity C₂ (#7).

The judgment unit 27 judges whether the region of interest in the imageI₂ is similar to the region of interest in each of the imagescorresponding to the similar case information sets B₁, and B₂, based oncomparison of the characteristic quantity C₂ with the characteristicquantity in each of the similar case information sets B₁ and B₂.Thereafter, the judgment unit 27 judges the degree of conformity of thesimilar case information sets A₁ to A₄ and B₁, and B₂ with the searchconditions, that is, the priority as similar cases to the images I₁ andI₂ (#12).

More specifically, the difference is found between the characteristicquantity C₂ and the characteristic quantity in each of the similar caseinformation sets B₁ and B₂. In the case where the difference is thepredetermined threshold value or smaller, the judgment unit 27 judgesthat the region of interest in the image I₂ is similar to the region ofinterest in the image corresponding to each of the similar caseinformation sets. In this case, assume that the similar case informationset B₁ has been judged to be “similar” while the similar caseinformation set B₂ has been judged to be “dissimilar”.

The judgment unit 27 further judges the degree of conformity of thesimilar case information sets A₁ to A₄ and B₁ and B₂ with the searchconditions, that is, the priority as the similar cases to the images I₁and I₂. FIG. 6 shows an example of judgment on the degree of conformity,and shows results of judgment on the similarity of the content-basedcharacteristic to the search target images I₁ and I₂ at the contrastenhancement phases P_(a) and P_(b), for each of the examination IDs ofthe respective similar case information sets A₁ to A₄ and B₁ and B₂.Assume that the examination IDs of the similar case information sets A₁(B₁), A₂ (B₂), A₃, and A₄ are “001”, “002”, “003”, and “004”,respectively. In this example, the judgment unit 27 judges that thesimilar case information set A₁ (B₁) having the examination ID “001” andhaving the similar content-based characteristic at the phases P_(a) andP_(b) has the highest degree of conformity (that is, priority “1”). Thejudgment unit 27 judges that the similar case information set A₃ havingthe examination ID “003” and having the similar content-basedcharacteristic at the phase P_(a) but leading to no similar caseinformation sets at the phase P_(b) has the second-highest degree ofconformity (priority “2”). The judgment unit 27 also judges that thesimilar case information set A₄ having the examination ID “004” andhaving the similar content-based characteristic at the phase P_(a) butleading to no similar case information sets (at the other contrastenhancement phase) of the same examination ID has a third highest degreeof conformity (priority “3”). The judgment unit 27 further judges thatthe similar case information set A₂ (B₂) having the examination ID “002”and having the similar content-based characteristic at the phase P_(a)but having no similar content-based characteristic at the phase P_(b)has the lowest degree of conformity (priority “4”). The similar caseinformation sets having the examination ID “002” are judged to have thelower degree of conformity than for the examination IDs “003” and “004”,since changes in the content-based characteristic associated with thetime elapsed after infusion of a contrast material are judged to bedifferent in the region of interest between the examination in which theimages I₁ and I₂ were obtained and the examination represented by theexamination ID “002”, based on the results of judgment on similarity atthe respective phases. Therefore, the case of the examination ID “002”can be judged affirmatively to show lower similarity than the cases ofthe examination IDs “003” and “004” having no similar case informationset for one of the phases (P_(b)) and thus enabling no such judgment.The similar case information set having the examination ID “003” isjudged to have the higher degree of conformity than the similar caseinformation set having the examination ID “004”, since the case of theexamination ID “003” has no similar case information set at the phaseP_(b) alone but the similar case information set at another one of thephases in the same examination exists. Therefore, once the similar caseinformation sets of the examination ID “003” are obtained, the similarcase information sets are judged to have higher utility value than thecase of the examination ID “004” that has no similar case informationset at another contrast enhancement phase in the same examination. Inthe case where the similar case information sets having the samepriority but different examination IDs exist, the degree of conformityis judged to be higher if the difference in the characteristic quantityat the contrast enhancement phase P_(a) is smaller.

The result of the similar case search is finally displayed on thedisplay of the workstation 3 (#13). A list of the similar caseinformation sets with the priority thereof may be displayed as shown inFIG. 6. Alternatively, a list of the similar case information setssorted in order of the priority may be displayed. When the physicianselects a desired one of the examination IDs from the list, the imageinterpretation/diagnosis support information related to the examinationID is displayed. Alternatively, the image interpretation/diagnosissupport information related to the examination ID having the highestpriority may be displayed, instead of the list.

As has been described above, in the similar case search apparatus inthis embodiment of the present invention, the contrast enhancementinformation analysis unit 21 obtains the contrast enhancementinformation (the contrast enhancement phases) P_(a) and P_(b) of therespective search target images I₁ and I₂ from the accompanyinginformation of the images obtained at the different contrast enhancementphases in the same examination, and the similar case database 9 storingthe similar case information sets each including the examination ID, thecontrast enhancement information, the characteristic quantity, and theimage interpretation/diagnosis support information is searched in theprocessing by the first similar case information search unit 25, thesecond similar case information search unit 26, and the judgment unit27, for obtaining the similar case information sets satisfying the threesearch conditions comprising agreement of the contrast enhancementphases with the search target images, agreement of the examinationbetween the similar case information sets, and similarity of thecontent-based characteristic to the search target images. Therefore, byeffectively using the images at the different contrast enhancementphases in the same examination, which have not conventionally been used,accuracy of the search for similar cases improves. Therefore, thisimprovement contributes to reduction in errors in judgment at the timeof image interpretation or diagnosis, such as erroneous judgment causedby incapability to detect a difference of a lesion from veins.

For example, as has been described above, in an examination of livertumor, an amount of absorbed X rays (CT values) in a tumor regionchanges in a complex manner according to the time elapsed. Therefore,detection of a tumor region has been difficult. However, in the similarcase search in the present invention, by using images obtained alongwith the time elapsed, information on cases showing similar complexchanges can be obtained. Therefore, accuracy of tumor detection by imageinterpretation and diagnosis can be improved.

More specifically, the first similar case information search unit 25obtains regarding the search target image I₁ the similar caseinformation sets A₁ to A₄ having the same contrast enhancement phaseP_(a) as the first search target image I₁ and having the characteristicquantity related to the contrast enhancement phase P_(a) whosedifference from the characteristic quantity C₁ of the first searchtarget image I₁ is the predetermined threshold value or smaller. Thesecond similar case information search unit 26 then obtains the similarcase information sets B₁ and B₂ having the same examination IDs as thesimilar case information sets A₁ to A₄ and having the same contrastenhancement information as the contrast enhancement phase P_(b) of thesecond search target image I₂, and the judgment unit 27 extracts thesimilar case information set B₁ whose characteristic quantity isdifferent from the characteristic quantity C₂ of the second searchtarget image I₂ by the predetermined threshold value or smaller, fromthe similar case information sets B₁ and B₂. Therefore, the similar caseinformation sets as a target of judgment by the judgment unit 27 on thesimilarity of the content-based characteristic to the second searchtarget image I₂ are limited to the information sets (B₁ and B₂) havingthe same examination IDs as the similar case information sets (A₁ to A₄)that satisfy the search conditions of similarity in the content-basedcharacteristic and agreement of the contrast enhancement phase to thefirst search target image I₁. Consequently, the number of times ofsimilarity judgment processing on the content-based characteristic,which imposes a heavy processing load, can be reduced and fasterprocessing can be realized.

Upon judgment on the degree of conformity with the search conditions,the judgment unit 27 also lowers the degree of conformity for the casewhere the similar case information set corresponding to the first searchtarget image I₁ exists but no similar case information set showing thesimilarity in the content-based characteristic corresponding to thesecond search target image I₂ exists although the similar caseinformation set satisfying the conditions of agreement in the contrastenhancement phase and the examination ID does exist for the secondsearch target image I₂ than for the case where the similar caseinformation set corresponding to the first search target image I₁ existsbut no similar case information set showing agreement of the contrastenhancement phase or the examination ID exists for the second searchtarget image I₂. By considering the degree of conformity in this manner,the judgment unit 27 distinguishes the two cases. Therefore, the degreeof conformity is lowered for the former case where the similar caseinformation sets are not thought to represent similar cases inconsideration of the time elapsed in the examination than for the lattercase where the pictorial similarity deserves consideration although thetime elapsed in the examination cannot be considered. Consequently, thesimilar case information sets can be provided in more detailedconsideration, as has been described above.

In addition, instead of the medical image itself, the characteristicquantity representing the content-based characteristic of the region ofinterest in the medical image is registered, as the characteristicinformation in each of the similar case information sets stored in thesimilar case database 9. Therefore, the characteristic quantity does notneed to be calculated at the time of search by the first similar caseinformation search unit 25 and at the time of judgment by the judgmentunit 27. Consequently, a processing load can be reduced.

Moreover, the ROI setting unit 22 obtains the information R₁ and R₂ ofthe regions of interest as important parts in the corresponding images,and the first similar case information search unit 25 and the judgmentunit 27 judge the similarity of the content-based characteristic for themore important parts. Consequently, more appropriate similar cases canbe searched for, which contributes to improvement in accuracy of imageinterpretation/diagnosis.

A modification to the embodiment described above will be described next.

In the above embodiment, the physician observes the images I₁ and I₂ asthe interpretation targets at the different contrast enhancement phasesdisplayed on the display of the workstation 3. However, even in the casewhere the physician obtains and displays only either one of the images(the image I₁, for example) for observation thereof, similar case searchincluding the image obtained at the different contrast enhancement phasein the same examination as the displayed image can be considered. FIG. 7is a block diagram showing the configuration of a similar case searchapparatus realizing such similar case search. As shown in FIG. 7, theapparatus comprises an examination ID analysis unit 28, anidentical-examination image search unit 29, and a second search targetimage determination unit 30, in addition to the configuration of theabove embodiment shown in FIG. 2.

The examination ID analysis unit 28 analyses general examinationinformation as a part of the accompanying information of the medicalimage data set conformed to the DICOM standard having been inputtedthereto, and obtains the examination ID. The examination ID analysisunit 28 stores the examination ID in the memory of the workstation 3.

The identical-examination image search unit 29 is installed in theworkstations 3, the image information management server 4, and the imageinformation database 5. More specifically, the identical-examinationimage search unit 29 carries out the following procedures. Theworkstation 3 requests viewing from the image information managementserver 4 by using the examination ID inputted thereto as a search key,and the image information management server 4 having received thisrequest searches the image information database 5 for obtaining files ofimages related to the same examination ID as the inputted examinationID, that is, the images as candidates for the second search targetimage. The image information management server 4 sends the image filesto the workstation 3 that sent the request, and the workstation 3receives the image files.

The second search target image determination unit 30 determines one ofthe images at the contrast enhancement phase different from the firstsearch target image as the second search target image, by using thecontrast enhancement information of the first search target image andthe contrast enhancement information of the candidate images for thesecond search target image.

In the above configuration including the units 28 to 30, the followingprocedures are carried out between Steps #5 and #6 in FIG. 4. Afterselection of the item “similar case search” (#5; YES), the examinationID analysis unit 28 analyses the accompanying information of the imageI₁ and obtains an examination ID E₁ thereof. The identical-examinationimage search unit 29 searches the image information database 5 by usingthe examination ID E₁ as the search key, and obtains images I₂ and I₃obtained in the same examination as the image I₁. The contrastenhancement information analysis unit 21 analyses the accompanyinginformation of the files of the images I₂ and I₃, and obtains theinformation of the contrast enhancement phases P_(b) and P_(a) of therespective images. The second search target image determination unit 30compares the contrast enhancement phase P_(a) of the image I₁ as thefirst search target image with the contrast enhancement phases P_(b) andP_(a) of the images I₂ and I₃ obtained by the identical-examinationimage search unit 29, and determines the image I₂ having the differentcontrast enhancement phase as the second search target image. At Step #6in FIG. 4, the second search target image I₂ determined by the secondsearch target image determination unit 30 is used as a target ofprocessing by the ROI reflecting unit 23. The procedures other than theprocedures described above are the same as the above embodiment.

In this manner, even in the case where a medical image observerrecognizes only the first search target image I₁, the similar casesearch including the second search target image I₂ at the differentcontrast enhancement phase in the same examination as the first searchtarget image I₁ can be realized. Consequently, accuracy of imageinterpretation and diagnosis improves.

In the above embodiment, when the judgment unit 27 judges the similarityof the content-based characteristic by using the difference between thecharacteristic quantity in each of the similar case information sets B₁and B₂ and the characteristic quantity C₂ of the second search targetimage I₂, differences in the characteristic quantity may be foundbetween the similar case information set B₁ and the similar caseinformation set A₁ having the same examination ID as the similar caseinformation set B₁ and between the similar case information set B₂ andthe similar case information set A₂ having the same examination ID asthe information set B₂ (denoted by Δ₁ and Δ₂, respectively). In thiscase, a difference is found between the characteristic quantities C₁ andC₂ of the first search target image I₁ and the second search targetimage I₂ (denoted by Δ₀), and the content-based characteristic is judgedto be “similar” in the case where a difference between these differences(that is, Δ₀-Δ₁ and Δ₀-Δ₂) is a predetermined threshold value orsmaller. In this case, the similarity can be judged by more stronglyreflecting a change in the images at the different contrast enhancementphases, which improves accuracy of the search.

In the case where a plurality of characteristic quantities are used, anoverall characteristic quantity may be found by weighting values of thecharacteristic quantities so that the judgment can be made based on apredetermined criterion for the overall characteristic quantity.Alternatively, the values of the characteristic quantities may be usedas multi-dimensional characteristic quantities so that the judgment onthe similarity can be made according to a distance in amulti-dimensional space.

At the time of judgment of the similarity in the content-basedcharacteristic, up to a predetermined number of the similar caseinformation sets sorted in order of smaller difference of thecharacteristic quantity from the characteristic quantity C₁ in theregion of interest in the search target image I₁ may be judged to be“similar”.

In the above embodiment, the physician manually sets the region ofinterest in the image I₁ by use of the ROI setting unit 22. However, alesion candidate region in the image I₁ may be automatically detectedand used as the ROI information R₁. In this case, upon display of theimage I₁ on the display, the detected candidate region may be displayedin an identifiable manner such as marking thereon. Alternatively, theautomatic detection processing and display of a detection result may becarried out in the case where a menu item “automatic detection resultdisplay” is selected by use of the mouse or the like from the userinterface displayed on the display. A method of the automatic detectionmay be a known method described in Japanese Unexamined PatentPublication No. 2005-198887 or 2005-246032, for example. In the casewhere a plurality of lesion candidate regions have been found throughthe automatic detection, the physician may select one of the candidateregions as the ROI information R₁. Alternatively, a user interface forcorrecting the automatically detected candidate regions may beinstalled. If the region of interest in the interpretation target imageI₁ is automatically detected in this manner, a burden on the imageinterpreter can be reduced, and oversight of a lesion can also bereduced. Even in the case where the region of interest is manuallyspecified as has been described above, the automatic detectionprocessing may be combined. For example, the physician may specify arectangular region including a lesion candidate. In this case, a regionof lesion candidate is detected automatically in the specified regionand used as the region of interest.

In addition, as shown in FIG. 8, the similar case database 9 may have anindex table representing the contrast enhancement phases of therespective similar case information sets shown for each of theexamination IDs thereof. In this case, before the processing by thefirst similar case information search unit 25 and the second similarcase information search unit 26, the index table is searched by usingthe contrast enhancement phase information P_(a) and P_(b) of the searchtarget images I₁ and I₂ as search keys, for screening for theexamination IDs having the contrast enhancement information representingthe both phases. The first similar case information search unit 25 thencarries out the search on the similar case information sets having theexamination IDs that have been found. In this manner, a processing loadon the first similar case information search unit 25 can be reduced.

In the above embodiment, the similar case search processing using thetwo search target images has been described. However, the similar casesearch processing of the present invention can be carried out in thesame manner for the case where three or more search target images atdifferent time phases (the contrast enhancement phases) are used.

Various modifications within the scope of the present invention to thesystem configuration, the processing flow, the database structure, theuser interface, and the like of the above embodiment are also includedin the scope of the present invention. The embodiment described above ismerely an example, and the description above should not be used to limitthe scope of the present invention. For example, the data structureshown in FIG. 3B may be used for the similar case database 9, while theimage interpretation/diagnosis support information in the table 9 c mayinclude the medical image data sets. In addition, the contrastenhancement information may be a portion of the accompanying informationof each of the medical image data sets, instead of an item in the table.

1. A similar case search apparatus comprising: a similar case databasestoring similar case information sets each including: examinationidentification information identifying an examination for obtaining amedical image; time phase information representing each of time phasesin the case where a plurality of medical images at the respective timephases are obtained in the examination; characteristic informationrepresenting a content-based characteristic of at least a region in themedical image; and image interpretation/diagnosis support informationfor supporting interpretation of a medical image the content-basedcharacteristic of which is similar thereto and/or for supportingdiagnosis based on the medical image having the similar content-basedcharacteristic, while relating the time phase information of each of thetime phases to the examination identification information and relatingthe characteristic information to the time phase information of each ofthe time phases; time phase information acquisition means for obtainingtime phase information representing different time phases of a pluralityof search target images obtained at the time phases in an examination,the time phase information which is obtain from accompanying informationadded to the respective search target images; and similar case searchmeans for carrying out a search of the similar case database for atleast the image interpretation/diagnosis support information in acorresponding portion of the similar case information sets satisfyingall of search conditions comprising: a first search condition that thetime phase information representing the respective time phases of thesearch target images exists; a second search condition that the timephase information representing the respective time phases is related tothe examination identification information representing one and the sameexamination; and a third search condition that the characteristicinformation related to the time phase information representing each ofthe time phases represents similarity in the content-basedcharacteristic to at least a region in a corresponding one of the searchtarget images at the corresponding time phase.
 2. The similar casesearch apparatus according to claim 1, wherein the similar case searchmeans carries out the search according to the first to third searchconditions by: obtaining a corresponding portion of the similar caseinformation sets having the time phase information representing the timephase of a first search target image as one of the search target imagesand representing that the characteristic information related to the timephase information thereof shows similarity in the content-basedcharacteristic to at least a region in the first search target image;and by extracting a corresponding portion of the similar caseinformation sets having the time phase information representing the timephase of a second search target image different from the first searchtarget image and showing similarity in the content-based characteristicin the characteristic information related to the time phase informationto at least a region in the second search target image, from acorresponding portion of the similar case information sets having theexamination identification information representing the same examinationas the portion of the similar case information sets having beenobtained.
 3. The similar case search apparatus according to claim 2,wherein, upon judgment on the similarity of the content-basedcharacteristic to at least a region in the second search target image,the similar case search means extracts a corresponding portion of thesimilar case information sets representing that a difference in thecharacteristic information between the respective time phases thereof issimilar to a difference in the content-based characteristic of at leasta region between the first and second search target images from acorresponding portion of the similar case information sets having theexamination identification information representing the same examinationand having the time phase information representing the time phases ofthe first and second search target images.
 4. The similar case searchapparatus according to claim 1, wherein, upon judgment on a degree ofconformity with the first to third search conditions, the similar casesearch means lowers the degree of conformity in order of: (1) the casewhere a corresponding portion of the similar case information setssatisfying all the first to third search conditions exists for all thesearch target images; (2) the case where a corresponding portion of thesimilar case information sets satisfying all the first to third searchconditions exists for a portion of the search target images but acorresponding portion of the similar case information sets satisfyingthe first or second search condition does not exist for the remainingportion of the search target images; (3) the case where a correspondingportion of the similar case information sets satisfying all the first tothird search conditions exists for a portion of the search target imagesbut a corresponding portion of the similar case information setssatisfying the third search condition does not exist for the remainingportion of the search target images although a corresponding portion ofthe similar case information sets satisfying the first or second searchcondition exists for the remaining portion of the search target images.5. The similar case search apparatus according to claim 1, furthercomprising second search target image acquisition means for obtainingexamination identification information identifying the examination inwhich a first search target image as one of the search target images wasobtained and the information representing the time phase of the firstsearch target image from the accompanying information of the firstsearch target image and for obtaining a medical image having theaccompanying information including the examination identificationinformation representing that the medical image was obtained in the sameexamination as the first search target image and including theinformation representing the time phase different from the first searchtarget image as a second search target image.
 6. The similar case searchapparatus according to claim 1, wherein the characteristic informationin each of the similar case information sets is a characteristicquantity representing the content-based characteristic of at least aregion in the medical image, and the similar case search apparatusfurther comprises characteristic quantity acquisition means forobtaining a characteristic quantity representing a content-basedcharacteristic of at least a region in each of the search target images.7. The similar case search apparatus according to claim 1, wherein saidat least a region in the medical image is a region of interest in themedical image, and the similar case search apparatus further comprisesregion-of-interest setting means for setting a region of interest ineach of the search target images.
 8. The similar case search apparatusaccording to claim 7, wherein the region-of-interest setting meansdetects the region of interest in each of the search target images. 9.The similar case search apparatus according to claim 7, wherein theregion-of-interest setting means sets the region of interest in a secondsearch target image as one of the search target images different from afirst search target image as another one of the search target images, ata position corresponding to the region of interest set in the firstsearch target image, based on the region of interest set in the firstsearch target image.
 10. The similar case search apparatus according toclaim 1 further comprising display means for displaying the imageinterpretation/diagnosis support information obtained by the similarcase search means.
 11. A similar case search method comprising the stepsof: obtaining time phase information representing different time phasesof a plurality of search target images obtained at the respective timephases in an examination, the time phase information which is obtainedfrom accompanying information added to the respective search targetimages; and searching a similar case database storing similar caseinformation sets each including: examination identification informationidentifying an examination for obtaining a medical image; time phaseinformation representing each of time phases in the case where aplurality of medical images at the respective time phases are obtainedin the examination; characteristic information representing acontent-based characteristic of at least a region in the medical image;and image interpretation/diagnosis support information for supportinginterpretation of a medical image the content-based characteristic ofwhich is similar thereto and/or for supporting diagnosis based on themedical image having the similar content-based characteristic, whilerelating the time phase information of each of the time phases to theexamination identification information and relating the characteristicinformation to the time phase information of each of the time phases,for at least the image interpretation/diagnosis support information in acorresponding portion of the similar case information sets satisfyingall of search conditions comprising: a first search condition that thetime phase information representing the respective time phases of thesearch target images exists; a second search condition that the timephase information representing the respective time phases is related tothe examination identification information representing one and the sameexamination; and a third search condition that the characteristicinformation related to the time phase information representing each ofthe time phases represents similarity in the content-basedcharacteristic to at least a region in a corresponding one of the searchtarget images at the corresponding time phase.
 12. A recording mediumstoring a similar case search program causing a computer to execute theprocedures of: obtaining time phase information representing differenttime phases of a plurality of search target images obtained at therespective time phases in an examination, the time phase informationwhich is obtained from accompanying information added to the respectivesearch target images; and searching a similar case database storingsimilar case information sets each including: examination identificationinformation identifying an examination for obtaining a medical image;time phase information representing each of time phases in the casewhere a plurality of medical images at the respective time phases areobtained in the examination; characteristic information representing acontent-based characteristic of at least a region in the medical image;and image interpretation/diagnosis support information for supportinginterpretation of a medical image the content-based characteristic ofwhich is similar thereto and/or for supporting diagnosis based on themedical image having the similar content-based characteristic, whilerelating the time phase information of each of the time phases to theexamination identification information and relating the characteristicinformation to the time phase information of each of the time phases,for at least the image interpretation/diagnosis support information in acorresponding portion of the similar case information sets satisfyingall of search conditions comprising: a first search condition that thetime phase information representing the respective time phases of thesearch target images exists; a second search condition that the timephase information representing the respective time phases is related tothe examination identification information representing one and the sameexamination; and a third search condition that the characteristicinformation related to the time phase information representing each ofthe time phases represents similarity in the content-basedcharacteristic to at least a region in a corresponding one of the searchtarget images at the corresponding time phase.